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Chapter 2. Definitions, design points, and key concepts 25
Model levels
A model level is defined as a subset of the system model that represents a
certain level of specificity (abstract to concrete); lower levels capture more
specific technology choices. Model levels are not levels of decomposition; in fact,
a model level can contain multiple levels of decomposition.
Model levels are elements designed to group artifacts with a similar level of detail
and are customizable to meet your needs and terminology. However, the levels
discussed in the following have proved to be useful in practice (Table 2-1).
Table 2-1 Model levels in the RUP SE architecture framework
Context level
The context level treats the entire system as a single entity, a black box. This
level addresses the system’s interaction with external entities.
Note that in Table 2-1 the system black box is a white-box view of the enterprise.
Understanding this shift in context is essential to success with MDSD. That is,
when we expand the enterprise black box to a white-box view, the system and
other entities in the enterprise will be represented. When we shift our focus to a
system
black box, the other entities will be its actors.
Analysis level
At the analysis level, the system’s internal elements are identified and described
at a relatively high level. Which elements are described at this level depends
upon the viewpoint. For example, in the logical viewpoint [see Table 2-2],
subsystems are created to represent abstract, high-level elements of
functionality. Less abstract elements are represented as sub-subsystems, or
classes. In the distribution viewpoint, localities are created to represent the
places where functionality is distributed.
Model level Expresses
Context System black box—the system and its actors (though this is a
black-box view of the system, it is a white-box view of the enterprise
containing the system)
Analysis System white box—initial system partitioning in each viewpoint that
establishes the conceptual approach
Design Realization of the analysis level in hardware, software, and people
Implementation Realization of the design model into specific configurations